Maybe add an assert system.version >= (3, 14) inside the except block?

You mentioned in python/cpython#119361 (comment) that you'd be adding a helper function for this kind of thing at some point -- would it be worth waiting for that, since the first 3.14 alpha is some way off?

I can also see the advantages of getting typing_extensions working with your branch, though, so that you can start testing with the rest of the ecosystem that depends on typing_extensions. So I definitely don't want to block you merging this.

I do expect we'll need more changes later, but it's helpful to get this merged so I can test the rest of the ecosystem too.